1. Field of the Invention:
This invention relates to a process for the processing of coal, heavy crude oil, bitumen or the like by heating the substances at specified temperatures and under specified pressures, followed by precipitation of hot sludge, whereby the hot sludge is further processed by stripping with gas.
2. Background Information:
Liquid hydrocarbons are separated on the basis of process-specific and product-specific conditions into products with different boiling ranges, such as gas, liquefied petroleum gas, gasoline, medium crude oil, heavy crude oil and residue by distillation. The bottom products of the distillation, so-called residues, are either converted to light products and separated as described above into product and residues, or used as fuel, such as heavy fuel oil and processed into bitumen.
In the prior art, the residues are distilled in vacuum plants at approximately 400.degree. C.-450.degree. C. and at 20 mbar-10 mbar. This process is the conventional one used in most refineries.
Extraction offers another possibility for separating hydrocarbons since the different solubility characteristics of liquids may be taken advantage of. The extraction agent dissolves the extract from a mixture of substances. The extraction agent is regenerated by the separation of the extract and injected in a process circuit. The separation can also take place by means of extraction or by means of distillation.
The prior art discloses supercritical extraction by means of processes for separation of paraffinic and aromatic hydrocarbons and hydrocarbon groups of asphalts. The extraction agents used are primarily components in the supercritical stage and, therefore, the partial pressures for mixtures must exceed certain specified critical values of temperature and pressure.
As an example, the critical values of several hydrocarbons are shown in the following table:
______________________________________ Critical Temp. .degree.C. Critical Pressure ______________________________________ H.sub.2 -240 13 Methane -82 46 Ethane 35 49 Propane 97 42 n-Butane 152 34 ______________________________________
The processes of the prior art exhibit significant disadvantages in practical applications. For example, some of the disadvantages inherent in the use of vacuum distillation plants are that:
1. The production of a vacuum requires a significant use of steam, and entails waste water problems.
2. The vacuum causes safety problems if there are leaks in the system causing possible oxygen infiltration and a danger of explosion.
3. As a result of the high temperature under which the process is conducted, coking problems may occur on account of unsaturated hydrocarbons, which on one hand have an effect on the product quality and on the other hand lead to operational problems. As a rule therefore, a maximum temperature of 450.degree. C. cannot be exceeded.
4. On account of the high-viscosity bottom products produced, there are discharge problems due to the lack of the required net positive suction head (NPSH) value on the extraction pump.
5. On account of the high velocities at the input (approximately 120 m/s), wear problems occur in valves and in the process column. Therefore, the systems may, eventually, require reinforcement.
6. Because of the employment of a vacuum and on account of the low vapor densities, large sized equipment, resulting in high investment costs, must be employed to limit the vapor velocity to technically acceptable values and to insure acceptable values of fluid discharge and pressure loss.
The disadvantages of the extraction process are that:
1. With these processes, substance-specific characteristics must be taken into consideration and, therefore, a special extraction agent must be found for each extract since no universal extraction agent exists.
2. The regeneration of the extraction agent is substance-specific and equipment-intensive. Regeneration can be performed by extraction, distillation and pressure change, combined with temperature changes.
3. On account of the expense of regeneration, there is a significant equipment expense and associated high investment cost.
4. On account of solubility equilibriums, there is always an extraction agent loss, which can lead to high operating costs.
The above-mentioned disadvantages of vacuum and extraction facilities can be reduced or even substantially, if not completely, eliminated by the use of the present invention.
German Laid Open Patent Application No. 31 23 535 discloses that separation of desired components can be done by stripping with gas. The change of partial pressure of the vapors necessary for product separation is achieved by the vacuum produced.